The present invention relates to a binocular, and more particularly, to a binocular including telescope optical systems that each include an erecting prism for erecting images.
Conventionally, a binocular includes two telescope systems, left and right. Each telescope system has, respectively, (at least) an objective lens, an erecting prism for erecting an inverse image that is imaged by the objective lens, and an eyepiece lens for observing the erected image.
In each telescope optical system, the erecting prism may be adjustable along the vertical and lateral directions with respect to an optical axis of the telescope optical system, so that the erected image, to be seen through the eyepiece optical lens, is formed inside a field stop, with a predetermined acceptable play. If the telescope optical system is a zoom system, the acceptable play takes into account various magnifying powers of the telescope optical system.
In particular, when a holder for holding the erected prism is installed in an attachment member, the location of the holding member with respect to the attachment member is adjusted so that the location of the erecting prism with respect to the optical axis can be adjusted properly.
In the conventional binocular, however, no particular adjustment structure or mechanism is provided, and such adjustment is made by means of inserted members that are difficult to arrange, such as shims, spacers, etc. That is, no adjustable structure or mechanism that is part of the binocular is provided, so that the adjustment of the erecting prism is both time-consuming and requires a high level of necessary skills. These drawbacks cause low productivity in manufacturing or repair.
Furthermore, in the conventional binocular, the location of the erecting prism with respect to the optical axis should be adjusted at the time of installation of the erecting prism to the attachment member, i.e., in the assembly stage. Therefore, when the location of the erecting prism requires later adjustment (e.g., due to independent reasons after the binocular is assembled, such correction of misalignment, or other repair or optimizing tasks), numerous parts other than the holding member and attachment member must be demounted in order to carry out the adjustment.
Still further, if the location of the erecting prism must be adjusted after the binocular has been assembled, any outer member covering the binocular must be removed so that the holding member and the attachment member can be adjusted as noted above, which also requires extra time and expense.